The shaft of one of the worse u-joints.. This one had no needle bearings left.

Last year my front drive shaft started squealing. Those of you who know me know my gripes with the local dealership in trying to get this fixed under warranty. On my last visit they went as far as to lie to my face and tell me they inspected it and couldn’t find anything wrong. Long story short, I pulled the drive shaft and replaced the u-joints and centering ball myself. As you can tell from the pictures taken shortly after my last trip to the dealership, they were rather destroyed.. It’s actually a pretty simple process, and a cheap u-joint tool from Princes Auto helped a lot… If only getting a dealership to do a proper warranty repair was this easy….

So, if you hear the angry sparrows a calling from your drive shaft, and lubricating does not help, replace those u-joints!

If you’re looking for a write-up on how to do this, I recommend Stu Offroad’s writeup: http://www.stu-offroad.com/axle/driveshaft/driveshaft-1.htm

The long weekend was a busy one with lots of progress made on the mini sumo. I sat down in front of the mill, and machined the robot’s body out of a single piece of 1″ thick Delrin, a task requiring a lot of care to not mess up, as one slip up has the potential to ruin the entire part, and hours of work.All in all, I think it turned out very well. Delrin machines very well, although does require a vacuum cleaner close by to continually clean up all the chips that accumulate, especially considering how much material I removed….

I also spun the two aluminum motor mounts, and cut the stainless steel base plate that seal off the bottom of the body. Still a lot of work to do on the chassis, and the circuit design is progressing slowly.. Now it’s just a race against time to get the PCBs made, circuits debugged, and a rudimentary program written up to get the robot running for the games. It’ll be tight, but I think It will be ready…

Here are some additional pictures…

Bottom view of the Chassis

Front view, with motor mounts and hub vissible

Milling out the inside of the Chassis, where the electronics and batteries will go

After 16 painful-to-wait hours, I cracked open the mold to check out the first prototype tire. It turned out very nicely, and much better than my previous adventures so many years ago. (Maybe when i get a chance I’ll dig up some of my old stuff to use as a comparison).

The traction on these tires is amazing, and the dark blue colour looks cool, however I think I’ll use a bit less pigment next time. The tricky part will be maintaining a consistent amount of pigment, since I only have one tire mold and will have to mix up a new batch for each tire I make. Making another mold would take valuable time away that I need to work on the chassis and electronics design if I’m to have any chance of finishing in time for the WCRG…

Note the air bubble that caused a missing piece in the tire.. Since this was a prototype tire that I plan to rip apart to test the strength, I wasn’t too concerned about fixing that part while molding it.

It’s been a while since my last post, but I’ve been working away hard at designing and a little bit of machining for my Mini Sumo. It’s proving to be quite a challenge to fit all the electronics and sensors I want into the small package of a mini sumo robot only 25mm tall, but I think I’ve figured out how to shoe-horn the electronics in there.

I’m planning to do some fairly sophisticated sensors, but that’s a topic for another day, and likely after the games as I likely have to run a temporary brain for this competition as time is too tight to get a PCB turn.

The finished tire mold

I have made decent headway on the chassis, having made more wheel blanks, and made a mold so that I can cast my own polyurethane tires. The mold itself is made from Delrin on the mill, held togethor by four screws, and kept in alignment with 6 dowel pins. The center slug was spun on a lathe, and forms the bottom of the mold, as well as a means to seat the wheel directly in the center of the mold. A top plate from scrap polycarbonate is screwed on to keep the top finish of the wheel nice.

Delrin is a really nice material to work with on a hobby mill and lathe, and it was relatively easy if somewhat time consuming to bore out the 25mm diameter hole for the robot.

Brushing on the Mold Release

6 or 7 years ago was the last time I cast polyurethane for sumo tires, I reckon, so I figured what I had lying around was no longer good. A bunch has changed since then, and a stop to a local mold making shop with some samples had me settled on Smooth-On Reoflex 30. Other people have used various Reoflex durometers for sumo robot tires as well. Feeling in a spendy mood, I also decided to buy some blue pigment.

Excitedly, at the end of the work day I got home with the polyurethane in it’s shiny box, which I’d bought over lunch hour, and prepared the mold. After collecting all the things I would need to cast my tires, I found that the really Old AIrbrus lying around wouldn’t spray the mold release agent anymore, so I cheated and used a brush instead. After waiting for the mold release to dry, I clamped the mold pieces together, popped in a wheel, and started mixing some polyurethane.

Ready to pour the polyurethane!

This new stuff works better than what I’d used previously, and was less viscous and as such did not get as many air bubbles trapped in it while mixing. An added benefit was that I could use some over-sized syringes I had lying from an old ink-jet cartridge re-filling kit.

A word of caution when using pigment for polyurethane, however: The “SoStrong” pigment.. Is, just as the name would imply, oddly, So Strong. I used a few drops, which was a few drops too many. The end result was a very dark mix. But, as this is a prototype tire that I plan to rip appart to test strength, I wasn’t too concerned.

Now the tire is sitting in the mold. With a 16 hour de-molding time, It should be ready tomorrow roughly around lunch… We shall see how it turned out then.

For now, here are some other links you may find useful with regards to polyurethane sumo tires:

Well, it’s been a while since I’ve updated, and I have gotten a little bit of work done on the robots in between ice diving adventures, and working on the Jeep. Most of the progress made has been playing with software (Investigating webcams and OpenCV for Spyder’s machine vision) and hardware design (PCB layouts for Spyder’s many circuits.)

Motor Mount Prototype

Motor Mount Prototype

Today, however, I sat down and got some machining work done for my mini sumo. I was wrestling (no pun intended) with the idea of how to mount the motors, and eventually decided to make a flanged sleeve for the motor to fit inside, which will then be securly attatched to the frame of the robot. The first attempt turned out pretty good, although not quite perfetct, as I didn’t properly square it off in one of the steps. It’s useable, but I’ll have to decide wether or not I want to make another one.

So, things are slowly comming a long. I’m afraid I won’t have all the circuitry I wanted to put into the mini sumo done in time for the robot games (chiefly goverened by the long lead time for budget PCB’s from batchPCB), but hopefully I can at least get something that will run arount the ring. I suppose as a backup, I do have my H-Bridge prototype board I could use to control it.. Complete with high-efficiency H-Bridge, and a powerful little 9s12 to control it all… Hmm..

I spent the past week and a bit diving in the Yucatan with my lovely girlfriend / dive-buddy-extraordinaire, and the warm water recreational diving oh so easy compared to what we contend with up here (We didn’t have to hike gear into a mountain lake, didn’t have to deal with cold water and plenty of insulation under drysuits requiring plenty of lead to sink, great visibility), and as always in warm water, there was so much amazing life to see. Great diving! It almost makes me want to move somewhere warmer.. But then if I lived somewhere warmer, I know I’d just look forward to vacations back up to Canada for the great west coast diving and rocky mountain lake diving…

Hangin' out on a safety stop

The funny thing that we both noticed about the cenote diving, however, is just how much of a striking resemblance the cavern areas resembled the walls at Horseshoe lake in Jasper. Granted that Horeshoe is a sort of a lake-based wall dive, and doesn’t have caverns or caves that we know about, but the rocks, tree limbs, small amount of life, etc, really did seem quite similar.

Now, after a nice warm vacation, we’re getting ready to do some local ice diving.. A bit of a shift, but that’s diving!

Anyways, just some rambling about my trip, and an appology-less explanation why there hasn’t been any progress on my robots in the past couple of weeks.

I received the remaining water-jet cut parts from Big Blue Saw a couple of weeks ago, and have slowly been working on taking them from rough water-jet cut pieces, to parts that will actually fit into the robot. The water-jet cuts are fairly rough when looking for precision parts, which is why a lot of work goes into the rough parts in order to get things to piece together nicely. To be honest, though.. I wish I had a CNC mill/router that I could have used to precisely cut the parts myself.

Water Jet Edge Finish

This isn’t to say that water-jet cutting is bad, but it is what it is. You have to account for the fact that water-jet cut parts aren’t 100% perfect to minute tolerances. Some of the issues I have with these parts are that the water-jet seems to have cut at a bit of an angle, which causes tolerance issues requiring some filing work to make sure everything fits together nicely. That said, I’m still happy overall with the water-jet cutting, and would recommend it to anyone trying to make more complicated shapes or numerous parts. I wouldn’t have been able to make all of the more complicated/curvy cuts by hand as precisely and quick as the water-jet service does. Plus, the edge finish has a pretty cool rough effect (Although I will be smoothing it out for this particular robot)

Four Legs!

After a lot of work machining the parts, I finally put togethor the frame of the robot with all four legs for the first time (minus the robot’s feet, which I haven’t gotten to yet). There’s still a lot of tweaking and some machining I have to do on these parts before they’re finished, and then there are a lot of small parts that I still have to make. It’s been around 5 months since I started this project, and things are really starting to come togethor, but I’m thinking it’ll still be another few months at least before the robot even moves, let alone moves in a fashion resembling autonomous walking. At least it’s finally starting to look like an actual quadrupedal walking robot.

Stepping the Axles

I also turned the axles on the lathe recently. Eight of the axles are simply straight 3mm shafts, however the four hip/base axles are 4mm in the center, and 3mm on either end with a center groove to hold an e-ring which is used to keep the flat-flex cable in place, and out of the gears. I still need to put the axles on the mill in order to flatten them out to keep set screws in place, and to drive the potentiometers I am using for axle position sensing. I’ll post more on those in the future when I get to that stage of the build

One of the other things I still need to complete are the motor controllers, and the actual robot’s brain (likely a Gumstix Overo, but I would have to make my own carrier baord). I have tweaked and fixed small bugs in the design of h-bridge prototype I built in the fall, however I want to move the same circuit into a shape that will fit into the actual upper-leg side piece. Luckily that gives me more space to work with than the current itteration of the board (which will be used for controlling the inner four motors), so it should be a relatively easy task once I find the time.

As with many projects, a mini sumo has been several years in the making, and has undergone several design revisions without actually having time to begin construction. But, finally, I took a bit of a break from the quadruped to start work on a mini sumo robot in the past couple days.

Start of a wheel

I had some round aluminum stock sitting around, and felt like playing around with the lathe. I got my trusty hack-saw out, cut off a chunk of aluminum, chucked it up on the lathe, and started spinning. Over the course of one evening, I came up with a basic wheel and hub assembly to go with the Maxon 17:1 gear motors I’ve had lying around for almost a year now, waiting for a sumo robot to be built around them. This is the same Maxon motor many people use, and I had to contend with the same issue, that the motor length itself is half the maximum width of a mini sumo robot (About 50mm). This called for making a hollow wheel that would slide over the motor.

I made a two piece assembly, with a hub that is attached to the motor with a set screw, and a wheel that is attached to the hub with several 2-56 screws.

Boring in Action

Overall, the boring went well on the lathe, but was definately a learning experience. The process itself was tedious, starting with drilling out a center hole using drill bits of incremental sizes until I had a center hole large enough to fit the boring tool, then slowly boring out a 21mm depth, 0.1-0.2mm at a time, slowing down as I approached the desired tolerance.

The tool itself chatters easily if you’re not careful, but I managed to produce a mostly clean bore. I’ll have to experiment/research a bit more on the best chip rates for turning aluminum stock…

Making the inner hub itself was easy to do, simply turning down the outside of a piece of aluminum, then using a couple drill bits to center drill a hole to about 2.85mm, then using a reamer to finish the center hole at a nice, clean 3mm to fit the shaft. A 4-40 set screw fit nicely, though I did have to file down a fraction of a millimeter that was sticking out from the hub itself, as that part of the hub fit with close tolerance into the wheel itself.

Prototype Wheel Parts

Prototype Wheel Assembly

Using a milling machine to precisely drill the holes that I would then use to tap and mount the actual wheel to the hub helped keep everything nice and accurate. Once finished, the wheel and hub aligned very well, and I had a completed wheel assembly.. Now to finish the other wheel, make a tire mold, mold the tires, mount the motors to a chassis, and make a brain for it all.. Hopefully I can have a basic robot ready in time for this year’s Robot Games.

The 2009 IEEE/WCRG Robot games have been announced for May 9th, 2009. I used to be an avid participant, but first school and then work travel got in the way and as such I’ve only managed to make it out once in the past few year.

This year, I’m hoping to have a mini-sumo ready in time, one that I’ve been designing in the back of my head for several months (years?) now. I’ve had some tiny Maxon motors sitting around that I bought a year ago with the hopes of finding time to start this robot, and today took a break from the quadruped to finally start machining the wheels. I’ll try and post details later.

Anyways, if you can make it out to Calgary for May 9th, it’s definatley worth checking out the Robot Games. If you have spare time, make a robot to compete! It doesn’t have to be perfect, it’s more fun building a robot than winning…